The reinforcement or reinforcing armature of tires, particularly motorcycle tires currently—and most often—consists of a stack of one or more plies conventionally known as “carcass plies”, “crown plies”, etc. This way of describing the reinforcements stems from the method of manufacture, which consists in creating a series of semi-finished products in the form of plies, provided with thread-like reinforcements, often longitudinal, which are subsequently assembled or stacked to build up a green tire. The plies are produced flat, to large dimensions, and then cut to suit the dimensions of a given product. At least some of the semi-finished products are assembled, to start off with, substantially flat. The green tire thus created is then shaped to give it the torroidal profile typical of tires. The so-called “finishing” semi-finished products are then applied to the green tire to obtain a product ready to be vulcanized.
A “conventional” type of method such as this entails, particularly in the phase of building up the green tire, the use of an anchoring element (generally a bead wire) which is used to anchor or hold the carcass reinforcement in the region of the beads of the tire. Thus, for this type of method, a portion of all the plies that make up the carcass reinforcement (or just part thereof) is folded back around a bead wire positioned in the bead of the tire. This then anchors the carcass reinforcement in the bead.
The widespread use within industry of this type of conventional product, in spite of there being numerous variations on the way in which the plies and assemblies are formed, has lead those skilled in the art to use vocabulary hinged on the method: hence the generally accepted terminology involving in particular the terms “plies”, “carcass”, “bead wire”, “shaping” to denote the progression from a flat profile to a torroidal profile, etc.
Nowadays there are tires which do not strictly speaking have any “plies” or “bead wires” conforming to the above definitions. For example, document EP 0 582 196 describes tires manufactured without the use of semi-finished products in the form of plies. For example, the reinforcing elements of the various reinforcing structures are applied directly to the adjacent layers of rubber compounds, all of this being applied in successive layers to a torroidal core the shape of which means that a profile likenable to the final profile of the tire being manufactured can be obtained directly. Thus, in such cases, there are no longer any “semi-finished products” or any “plies”, or any “bead wires”. The basic products, such as the rubber compounds and the reinforcing elements in the form of threads or filaments, are applied directly to the core. Because this core is of torroidal shape, there is no longer any need to build up a green tire to evolve from a flat profile to a torus-shaped profile.
Moreover, the tires described in that document do not have the “traditional” folding of the carcass ply back around a bead wire. This type of anchorage is replaced by an arrangement whereby circumferential threads are positioned adjacent to the said sidewall reinforcing structure, all of it embedded in an anchoring or bonding rubber compound.
There are also methods of assembly on a torroidal core that use semi-finished products that are specially designed for rapid, effective and simple laying onto a central core. Finally, it is also possible to use a hybrid comprising both some semi-finished products for creating certain architectural aspects (such as plies, bead wires, etc.) while others are created by applying compounds and/or reinforcing elements directly.
In this document, in order to take account of the recent technological advances both in the field of the manufacture and in terms of the design of the products, the conventional terms such as “plies”, “bead wires”, etc., are advantageously replaced with terms which are neutral or independent of the type of method used. Thus, the term “carcass-type reinforcement” or “sidewall reinforcement” is a valid way of denoting the reinforcing elements of a carcass ply in the conventional method and the corresponding reinforcing elements, generally applied in the sidewalls, of a tire produced according to a method that does not employ semi-finished products. The term “anchoring zone”, for its part, can just as easily denote the “traditional” folding-back of the carcass ply around a bead wire in a conventional method as it can the assembly formed by the circumferential reinforcing elements, the rubber compound, and the adjacent sidewall reinforcing portions of a bottom zone created using a method that involves application onto a torroidal core.
As in the case of all other tires, motorcycle tires are switching over to a radial design and such tires comprise a carcass reinforcement formed of one or two layers of reinforcing elements making angles that may range between 65° and 90° with the circumferential direction, the said carcass reinforcement being radially surmounted by a crown reinforcement formed at least of generally textile reinforcing elements. However, non-radial tires still remain and the invention applies equally to these. The invention also relates to partially radial tires, that is to say tires in which the reinforcing elements of the carcass reinforcement are radial over at least part of the said carcass reinforcement, for example in the part corresponding to the sidewall of the tire.
Numerous crown reinforcement designs have been proposed, according to whether the tire is intended to be mounted on the front of the motorbike or on the rear. A first structure consists, for the said crown reinforcement, in using only circumferential cords, and the said structure is more particularly used on the rear tire. A second structure, inspired directly by the structures commonly used for passenger vehicle tires, has been used to improve wear resistance, and consists in using at least two crown layers of reinforcing elements that are mutually parallel within each layer but cross from one layer to the next, making acute angles with the circumferential direction, such tires being more particularly suited to the front of motorbikes. The said two crown layers may be radially surmounted by at least one layer of circumferential elements, generally obtained by helically winding a strip of at least one rubber-coated reinforcing element. Patent FR 2 561 588 thus describes such a crown reinforcement, with at least one layer the reinforcing elements of which make an angle that may vary between 0° and 8° with the circumferential direction, the elastic modulus of such elements being as high as at least 6000 N/mm2 and, positioned between the carcass reinforcement and the layer of circumferential elements, a cushioning layer made up mainly of two layers of elements that are crossed from one layer to the next, making angles of between 60° and 90° with one another, the said crossed layers being formed of textile reinforcing elements with an elastic modulus of at least 6000 N/mm2.
U.S. Pat. No. 5,301,730, with a view to increasing the drive of a tire for a motorbike rear tire, proposes a crown reinforcement made up, from the radial carcass reinforcement to the tread, of at least one ply of substantially circumferential elements and of two plies of elements that cross from one ply to the next making an angle that may range between 35° and 55° with the circumferential direction, the ply of elements parallel to the circumferential direction possibly being made of aromatic polyamide elements and the plies of crossed elements of aliphatic polyamide.